The use of acidic leach media to leach sulphur, arsenic and telluride compounds of metals such as copper, iron, zinc, etc. is known. To date, much of the prior art has been devoted to the use of leach media comprising nitric acid and sulphuric acid at temperatures generally below 100.degree. C. Unfortunately, when such leach media are utilized under these conditions, a solution containing 100% of the metal can not be obtained.
U.S. Pat. No. 3,888,748 (Brennecke) discloses a process for recovering metal values from ore concentrates. Essentially, the process comprises contacting the ore concentrate with an aqueous solution of nitric and sulphuric acids to produce a mixture comprising a residue and a leachate. The leachate is further processed to recover copper and iron precipitated as jarosite. This process is deficient in that it requires the use of highly corrosive acids as the leach medium. Moreover, the solution of nitric and sulphur acids does not completely dissolve the concentrate.
U.S. Pat. No. 3,910,636 (Hard) discloses a process for in-situ mining. Specifically, the process comprises the use of an acidic leaching medium comprising nitrate ions and having a pH of from about 0.2 to about 2.0. The process comprises drilling at least one well into an underground formation or ore deposit and thereafter sealing at least a portion of the well. The leaching solution is then introduced into the wellbore and thereafter into the zone in the formation immediately surrounding the wellbore. Since the process involves in-situ mining, a relatively dilute concentration of nitrate ion and sulphuric acid is required. Not surprisingly, the dilute nature of the leaching medium necessitates relatively long residence time to obtain maximum copper loading in the leach medium. Even with such long residence time, the leaching medium does not completely dissolve the contacted copper ore.
U.S. Pat. No. 3,912,330 (Carnahan et al) discloses chemical mining of copper porphyry ores. Specifically, it is disclosed that the addition of catalytic amounts of nitrate ion added to an oxygenated sulphuric acid leach medium purportedly improves the rate of copper extraction from copper sulphides contained in porphyry ores. It is disclosed that the nitrate ion has the catalytic effect when present in concentrations of from 0.05 to 0.50% of the leach medium. During the process, any codissolved iron is precipitated as jarosite. Thus, the pregnant leach solution recovered in the process purportedly comprises very low iron concentration. "Oxygen pressure" is disclosed as being an important variable in the process. Preferred oxygen pressures are in the range 25 psi-200 psi. The preferred temperature in the leaching step is 100.degree. C. It is noteworthy that the patentee acknowledges that the subject process is not feasible for use in conventional surface heap leaching.
Indeed, the limitations of temperature and oxygen overpressure in conventional in-situ mining processes effectively exclude such processes from use in surface heap leaching applications.
It would be desirable to have a process for recovery of metal from a feedstock comprising copper and, optionally, at least one metal selected from the group consisting essentially of copper, iron, zinc, silver and gold. In cases where the feedstock comprises copper and iron, it would be desirable if the recovered iron was in a form other than jarosite which is a product of little or no value. It would also be desirable if such a process, when used in a batch-wise manner, was time efficient (e.g. minutes instead of hours).